C'est finalement un Duetto 1966! (et non un 1967)
Voici ce que j'ai trouvé sur le web qui le souligne: "The Graduate-car was a red 1966 1600 Duetto. Dustin Hoffman was related to the US Alfa-importer, so that's why the Duetto became a movie-star. They used two cars, both 1966 European versions. In the excellent book "Alfa Romeo Duetto Spiders" by Gienzano Madaro, you may read all about it. Publ. Giorgio Nada Editore, ISBN88-7911-063-2".

Regarding the issue of the headlamp covers these are the facts as I understand them.

The US (1966-67) versions of the original 1600 'Duetto' were not fitted with the plexilens covers.

Later in 1968 (after the Graduate was filmed) the 1300 'Junior' Spider was introduced. These also had headlamps without these plexilens covers. As far as I'm aware the 1300 Juniors were mainly intended for European use. I doubt they were sold in the USA.

The headlamp chromed bezels on the US 'Duetto' was noticably thicker than the 'Junior' headlamp bezels. These thicker bezels are shown on the 'Graduade' car.

Despite the comments made in the book "Alfa Romeo Duetto Spiders" by Gienzano Madaro, the 'Graduate' car (or cars) was a 1966 'Duetto' made or later modified for the US market as it was without the headlamp covers.

I always wondered why clear headlamp covers were never used on import cars in the US. There are more examples, like the Jaguar E-Type, Fiat 850 Spider, Citroen DS and SM and others. My guess always was they were illegal (plexiglass ones were in Germany for example), but that theory is contradicted by the clear covers on the headlamps of the 1964-66 Imperials. Maybe they just didn't work with the standard sealed-beam headlamps used on imports for the US?

junkman, I believe you're right about the covers becoming illegal in the USA. The FMVSS regulations introduced by the US started in the mid-1960s I believe. I cannot remember the exact year but certainly by 1968 they were well established.

Looking at the old brochures for the USA XK-E type Jaguars, they appear to show that the curved plastic covers were even used on US cars from 1961 to 1966. By 1969 I remember that the US Jaguar XK-E type was re-styled without the covers. So it's not impossible therefore that the Imperial 1964-66 escaped the regulations.

It's common for the car manufacturers to have 3 or more years advance notice of a regulation being implimented. So they may choose to impliment changes early rather than wait for re-stying. European cars did not have the one-year design cycle that was common in the US in the 1960s.

I don't normally read IMCDB but found this thread, and thought it might be helpful if the open questions were answered. Hence, I registered, in order to post... Here are some points which I hope will clear up some of the questions.

1. 1968 was the last year in which the U.S. allowed covered headlights. (This is well documented in the U.S. Jaguar Club forums.)
2. Alfa did not export any cars to the U.S.A. in 1968. This was because Alfa already knew that the Spiders with carburetors could not meet U.S. regulations and decided that U.S. Spiders would be fitted with the SPICA mechanical fuel injection, instead of carburetors. The SPICA was not ready in until 1969, and the first SPICA Spiders came over in February of 1969.
3. U.S. Spiders from 1966 and 1967 came with the Carello headlight cover kits in the trunk, for dealers to install.
4. The reason the kits Carello kits came in the trunk was because of concerns during shipping. The covers do scratch, and there was concern that they could break. (It has not been uncommon for cars to get damaged during transport, and all car manufacturers have very talented people that fix new cars. Needless to say, this is expensive.)
5. The 1969 Spider also came with the Carello kit in the trunk, and the dealers did not install them, because it was illegal to do so. Of course, the owners could install them.
6. Some owners did order 1968 Spiders through Canada and brought them into the U.S. These models have carburetors and also had the Carello kit in the trunk.